1. Field
An embodiment of the present invention relates to a current generator and an organic light emitting display using the same.
2. Description of the Related Art
Recently, various flat panel displays (FPD) with reduced weight and volume in comparison to cathode ray tube (CRT) type displays have been developed. The FPDs include liquid crystal displays (LCD), field emission displays (FED), plasma display panels (PDP), and organic light emitting displays.
Among the FPDs, the organic light emitting displays display images using organic light emitting diodes (OLED) that generate light by re-combination of electrons and holes. The organic light emitting display has high response speed and is driven with low power consumption.
FIG. 1 is a schematic circuit diagram illustrating a pixel of a conventional organic light emitting display.
Referring to FIG. 1, a pixel 4 of the conventional organic light emitting display includes an organic light emitting diode OLED and a pixel circuit 2 coupled to a data line Dm and a scan line Sn to control the OLED.
The anode electrode of the OLED is coupled to the pixel circuit 2, and the cathode electrode of the OLED is coupled to a second power source ELVSS. The OLED emits light with a brightness corresponding to the current supplied from the pixel circuit 2.
The pixel circuit 2 controls the amount of current supplied to the OLED to correspond to a data signal supplied to the data line Dm when a scan signal is supplied to the scan line Sn.
Here, the pixel circuit 2 includes a second transistor M2 coupled between a first power source ELVDD and the OLED, a first transistor M1 coupled to the second transistor M2, the data line Dm, and the scan line Sn, and a storage capacitor Cst coupled between the gate electrode and the first electrode of the second transistor M2.
The gate electrode of the first transistor M1 is coupled to the scan line Sn, and its first electrode is coupled to the data line Dm. Then, the second electrode of the first transistor M1 is coupled to one terminal of the storage capacitor Cst.
Here, the first electrode is set as one of a source electrode and a drain electrode, and the second electrode is set as a different electrode from the first electrode. For example, when the first electrode is set as the source electrode, the second electrode is set as the drain electrode. The first transistor M1 coupled to the scan line Sn and the data line Dm is turned on when a scan signal is supplied from the scan line Sn to supply a data signal supplied from the data line Dm to the storage capacitor Cst. Here, the storage capacitor Cst is charged with a voltage corresponding to the data signal.
The gate electrode of the second transistor M2 is coupled to one terminal of the storage capacitor Cst, and its first electrode is coupled to the other terminal of the storage capacitor Cst and the first power source ELVDD. Then, the second electrode of the second transistor M2 is coupled to the anode electrode of the OLED.
The second transistor M2 controls the amount of current supplied from the first power source ELVDD to the second power source ELVSS via the OLED to correspond to the voltage value stored in the storage capacitor Cst. Here, the OLED generates light corresponding to the amount of the current supplied from the second transistor M2.
However, the above-described conventional organic light emitting display cannot display an image with desired brightness due to a change in efficiency in accordance with deterioration of the OLED.
As time passes, the OLED deteriorates so that light generated by the OLED gradually has lower brightness corresponding to the same data signal. In addition, in the conventional art, due to non-uniformity in the threshold voltage/mobility of the driving transistor M2 included in each of the pixels 4, an image with uniform brightness may not be displayed.